Television is used to deliver entertainment and education to viewers. The source material (audio, video, etc.) is multiplexed into a combined signal which is then used to modulate a carrier. This carrier is commonly known as a channel. (A typical channel can carry one analog program, one or two high definition (HD) digital program(s), or several (e.g. nine) standard definition digital programs.) In a terrestrial system, these channels correspond to government assigned frequencies and are distributed over the air. The program is delivered to a receiver that has a tuner that pulls the signal from the air and delivers it to a demodulator, which in turn provides video to a display and audio to speakers. In a cable system the modulated channels are carried over a cable. There may also be an in-band or out-of-band feed of a program guide indicating what programs are available and the associated tuning information. The number of cable channels is finite and limited by equipment/cable bandwidth. Cable distribution systems require a significant capital investment and are expensive to upgrade.
Much of television content is valuable to its producers, therefore copyright holders want to control access and restrict copies. Examples of typically protected material include feature films, sporting events, and adult programming. Conditional access (CA) systems are used to control availability of programming in content delivery systems such as cable systems. CA systems come as matched sets—one part is integrated into the cable system headend and encrypts premium content, the other part provides decryption and is built into the set-top boxes (STB) installed in user's homes. Several CA systems are used in the cable industry including those provided by NDS (Newport Beach, Calif.), Motorola (Schaumberg, Ill.) and Scientific Atlanta (Atlanta, Ga.). This matched set aspect of CA systems has the effect that the “legacy” vendor is locked in as the supplier of additional STBs. Since the various technologies for conditional access are not mutually compatible (and are often proprietary), any new potential supplier is forced to license the legacy CA. Thus, the cable operator finds itself unable to acquire newer technology or competing technology from other set-top box manufacturers since the technology owners are often unwilling to cooperate, or charge reasonable license fees. This inflexibility can be especially troublesome when cable companies with disparate CA systems are merged. Service providers would like more than one source for STBs for any number of reasons.
Once a cable operator picks an encryption scheme, it is difficult to change or upgrade the content encryption scheme without introducing a backward compatible decoding device (e.g. set-top box). Providing multiple mode capability in new set-top boxes to handle multiple encryption systems can add substantial cost to any new set-top box, providing that the technology can be made available to the STB vendor to provide the multiple decryption capability.
The only known current option to avoiding domination by the legacy vendor (short of wholesale replacement) is using “full dual carriage”. Full dual carriage means that transmission is duplicated for each encrypted program—once for each type of CA encryption to be used. To provide full dual carriage, the headend is enhanced to provide each form of CA simultaneously. Legacy STBs should not be impacted and should continue to perform their function despite any change. However, full dual carriage often comes at an unpalatable price because of the bandwidth impact, thus reducing the number of unique programs available. Generally, the number of premium channels suffers so that the number of options available to the viewer are limited and the value that can be provided by the cable operator is restricted.
A conventional cable system arrangement is depicted in FIG. 1. In such a system, the cable operator processes audio/video (A/V) content 14 with CA technology from manufacturer A (system A) using CA encryption equipment 18 compliant with system A at the cable system—headend 22. The encrypted A/V content along with system information (SI) 26 and program specific information (PSI) 27 is multiplexed together and transmitted over the cable system 32 to a user's STB 36. STB 36 incorporates decrypting CA equipment from system A (manufacturer A) 40 that decrypts the A/V content. The decrypted A/V content can then be supplied to a television set 44 for viewing by the user.
In a cable system such as that of FIG. 1, digital program streams are broken into packets for transmission. Packets for each component of a program (video, audio, auxiliary data, etc.) are tagged with a packet identifier or PID. These packet streams for each component of all programs carried within a channel are aggregated into one composite stream. Additional packets are also included to provide decryption keys and other overhead information. Otherwise unused bandwidth is filled with null packets. Bandwidth budgets are usually adjusted to utilize about 95% of the available channel bandwidth.
Overhead information usually includes guide data describing what programs are available and how to locate the associated channels and components. This guide data is also known as system information or SI. SI may be delivered to the STB in-band (part of the data encoded within a channel) or out-of-band (using a special channel dedicated to the purpose). Electronically delivered SI may be partially duplicated in more traditional forms—grids published in newspapers and magazines.
In order for a viewer to have a satisfying television experience, it is generally desirable that the viewer have clear access to both audio and video content. Some analog cable systems have used various filtering techniques to obscure the video to prevent an unauthorized viewer from receiving programming that has not been paid for. In such a system, the analog audio is sometimes sent in the clear. In the Motorola VideoCipher 2 Plus system used in C-band satellite transmissions, strong digital audio encryption is used in conjunction with a relatively weak protection of the analog video (using sync inversion). In airline in-flight movie systems, the availability of audio only through rental of headphones has been used to provide the full audio and video only to paying customers.